Organic light emitting diode display device and method of fabricating the same

ABSTRACT

An organic light emitting diode display device includes a first substrate including a display region, wherein a plurality of pixel regions are defined in the display region; a first electrode over the substrate and in each of the plurality of pixel regions; a bank on edges of the first electrode and surrounding each of the plurality of pixel regions, the bank including a lower layer having a hydrophilic property and an upper layer having a hydrophobic property; an organic emitting layer on the first electrode and in each of the plurality of pixel regions surrounded by the bank; and a second electrode on the organic emitting layer and covering an entire surface of the display region.

The present application claims the benefit of Korean Patent ApplicationNo. 10-2012-0131546 filed in Korea on Nov. 20, 2012, which is herebyincorporated by reference for all purposes as if fully set forth herein.

BACKGROUND

Field of the Disclosure

The disclosure relates to an organic light emitting diode (OLED) displaydevice, which may be referred to as an organic electroluminescentdisplay device, and more particularly, to an OLED display device havinga bank of a double-layered structure and a method of fabricating thesame.

Discussion of the Related Art

An OLED display device of new flat panel display devices has highbrightness and low driving voltage. The OLED display device is aself-emitting type and has excellent view angle characteristics,contrast ratio, a response time, etc.

Accordingly, the OLED display device is widely used for a television, amonitor, a mobile phone, etc.

The OLED display device includes an array element and an organic lightemitting diode. The array element includes a switching thin filmtransistor (TFT), which is connected to a gate line and a data line, adriving TFT, which is connected to the switching TFT, and a power line,which is connected to the driving TFT. The organic light emitting diodeincludes a first electrode, which is connected to the driving TFT, andfurther includes an organic emitting layer and a second electrode.

In the OLED display device, light from the organic emitting layer passesthrough the first electrode or the second electrode to display an image.A top emission type OLED display device, where the light passes throughthe second electrode, has an advantage in an aperture ratio.

Generally, the organic emitting layer is formed by a thermal depositionmethod using a shadow mask. However, the shadow mask sags because theshadow mask becomes larger with an increase in sizes of display devices.As a result, there is a problem in deposition uniformity in the largerdisplay device. In addition, since a shadow effect is generated in thethermal deposition method using the shadow mask, it is very difficult tofabricate a high resolution OLED display device, e.g., above 250 PPI(pixels per inch).

Accordingly, a new method instead of the thermal deposition method usingthe shadow mask has been introduced.

In the new method, a liquid phase organic emitting material is sprayedor dropped in a region surrounded by a wall using an ink jet apparatusor a nozzle-coating apparatus and cured to form the organic emittinglayer.

FIGS. 1A and 1B are schematic cross-sectional views showing an OLEDdisplay device in steps of forming an organic emitting layer by sprayingor dropping a liquid phase organic emitting material.

To spray or drop the liquid phase organic emitting material by the inkjet apparatus or the nozzle-coating apparatus, a bank 53, which isformed on the first electrode 50 and surrounds a pixel region P, isrequired to prevent the liquid phase organic emitting material fromflooding into a next pixel region P. Accordingly, as shown in FIG. 1A,the bank 53 is formed on edges of the first electrode 50 before formingthe organic emitting layer 55.

The bank 53 is formed of an organic material including fluorine (F) suchthat the bank 53 has a hydrophobic property. The hydrophobic bank 53prevents the organic emitting material, which has a hydrophilicproperty, from being formed on the bank 53 and flooding into the nextpixel region P due to a mis-alignment of the ink jet apparatus or thenozzle-coating apparatus or an excessive amount of the organic emittingmaterial.

The bank 53 may be formed by a mask process, which includeslight-exposing and developing steps after the organic insulatingmaterial including fluorine is applied to an entire surface of thesubstrate 10.

Next, as shown in FIG. 1B, by spraying or dropping the liquid phaseorganic emitting material from a head of the ink-jet apparatus or anozzle of the nozzle-coating apparatus into the pixel region P, which issurrounded by the bank 53, the pixel region P is filled with the organicemitting material. The organic emitting material is dried and cured byheat to form the organic emitting layer 55.

However, fluorine residues 54 may remain in the pixel region P when thebank 53 is formed, and the fluorine residues 54 may hinder the liquidphase organic emitting material from being spread in the pixel region Pwhen the liquid phase organic emitting material is sprayed or dropped.Accordingly, as shown in FIG. 2, which is a picture showing a part ofone pixel region in the related art OLED display device, the organicemitting layer is not formed around the hydrophobic bank, or a portionof the organic emitting layer around the hydrophobic bank has a thinnerthickness than portions in other regions. Thus, dark images aredisplayed in edges of the pixel region. In addition, the OLED displaydevice is degraded fast due to the difference in thicknesses, and thelifetime of the OLED display device is shortened.

SUMMARY

An organic light emitting diode display device includes a firstsubstrate including a display region, wherein a plurality of pixelregions are defined in the display region; a first electrode over thesubstrate and in each of the plurality of pixel regions; a bank on edgesof the first electrode and surrounding each of the plurality of pixelregions, the bank including a lower layer having a hydrophilic propertyand an upper layer having a hydrophobic property; an organic emittinglayer on the first electrode and in each of the plurality of pixelregions surrounded by the bank; and a second electrode on the organicemitting layer and covering an entire surface of the display region.

In another aspect, a method of fabricating an organic light emittingdiode display device includes forming a first electrode over a firstsubstrate including a display region, which includes a plurality ofpixel regions, the first electrode formed in each of the plurality ofpixel regions; forming a bank on edges of the first electrode andsurrounding each of the plurality of pixel regions, the bank including alower layer having a hydrophilic property and an upper layer having ahydrophobic property; forming an organic emitting layer on the firstelectrode and in each of the plurality of pixel regions surrounded bythe bank; and forming a second electrode on the organic emitting layer,the second electrode covering an entire surface of the display region.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention.

FIGS. 1A and 1B are schematic cross-sectional views showing an OLEDdisplay device in steps of forming an organic emitting layer by sprayingor dropping a liquid phase organic emitting material.

FIG. 2 is a picture showing a part of one pixel region in the relatedart OLED display device.

FIG. 3 is a circuit diagram of one pixel region of an OLED device.

FIG. 4 is a schematic cross-sectional view of an OLED display deviceaccording to an embodiment of the present invention.

FIG. 5 is a schematic cross-sectional view of an OLED display deviceaccording to one modified embodiment of the present invention.

FIG. 6 is a schematic cross-sectional view of an OLED display deviceaccording to another modified embodiment of the present invention.

FIGS. 7A to 7H are cross-sectional views showing a fabricating processof an OLED display device according to an embodiment of the presentinvention.

FIGS. 8A to 8E are cross-sectional views showing a fabricating processof on OLED display device according to another example of the embodimentof the present invention.

DETAILED DESCRIPTION

Reference will now be made in detail to the preferred embodiments,examples of which are illustrated in the accompanying drawings.

FIG. 3 is a circuit diagram of one pixel region of an OLED device.

As shown in FIG. 3, an OLED display device includes a switching thinfilm transistor (TFT) STr, a driving TFT DTr, a storage capacitor StgCand an emitting diode E in each pixel region P.

On a substrate (not shown), a gate line GL along a first direction and adata line DL along a second direction are formed. The gate line GL andthe data line DL cross each other to define the pixel region P. A powerline PL for providing a source voltage to the emitting diode E is formedto be parallel to and spaced apart from the data line DL.

The switching TFT STr is connected to the gate and data lines GL and DL,and the driving TFT DTr and the storage capacitor StgC are connected tothe switching TFT STr and the power line PL. The emitting diode E isconnected to the driving TFT DTr.

A first electrode of the emitting diode E is connected to a drainelectrode of the driving TFT DTr, and a second electrode of the emittingdiode E is grounded.

When the switching TFT STr is turned on by a gate signal applied throughthe gate line GL, a data signal from the data line DL is applied to thegate electrode of the driving TFT DTr and an electrode of the storagecapacitor StgC. When the driving TFT DTr is turned on by the datasignal, an electric current is supplied to the emitting diode E from thepower line PL. As a result, the emitting diode E emits light. In thiscase, when the driving TFT DTr is turned on, a level of an electriccurrent applied from the power line PL to the emitting diode E isdetermined such that the emitting diode E can produce a gray scale. Thestorage capacitor StgC serves to maintain the voltage of the gateelectrode of the driving TFT DTr when the switching TFT STr is turnedoff. Accordingly, even if the switching TFT STr is turned off, a levelof an electric current applied from the power line PL to the emittingdiode E is maintained to a next frame.

FIG. 4 is a schematic cross-sectional view of an OLED display deviceaccording to an embodiment of the present invention. For convenience ofexplanation, a driving area (DA) wherein a driving TFT DTr is formed, apixel region P where an emitting diode E is formed, and a switching area(not shown) where a switching TFT (not shown) are defined.

As shown in FIG. 4, an OLED display device 101 of the present inventionincludes a first substrate 110, where the driving TFT DTr, the switchingTFT (not shown) and the emitting diode E are formed, and a secondsubstrate 170 for encapsulation. The second substrate 170 may be aninorganic insulating film or an organic insulating film.

A gate line (not shown) and a data line (not shown) are formed on thefirst substrate 110. The gate line and the data line cross each other todefine the pixel region P. A power line (not shown) for providing avoltage to the emitting diode E is formed to be parallel to and spacedapart from the data line.

In each pixel region P, the switching TFT is connected to the gate lineand the data line, and the driving TFT DTr and the storage capacitorStgC are connected to the switching TFT and the power line.

The driving TFT DTr includes a gate electrode 115, a gate insulatinglayer 118, an oxide semiconductor layer 120, an etch-stopper 122, asource electrode 133 and a drain electrode 136. The gate insulatinglayer 118 covers the gate electrode 115, and the oxide semiconductorlayer 120 is disposed on the gate insulating layer 118. The oxidesemiconductor layer 120 corresponds to the gate electrode 115. Theetch-stopper 122 covers a center of the oxide semiconductor layer 120.The source electrode 133 and the drain electrode 136 are disposed on theetch-stopper 122 and spaced apart from each other. The source electrode133 and the drain electrode 136 contact both ends of the oxidesemiconductor layer 120, respectively. Although not shown, the switchingTFT has substantially the same structure as the driving TFT DTr.

In FIG. 4, each of the driving TFT DTr and the switching TFT includesthe oxide semiconductor layer 120 of an oxide semiconductor material.Alternatively, as shown in FIG. 5, each of the driving TFT DTr and theswitching TFT may include a gate electrode 213, a gate insulating layer218, a semiconductor layer 220 including an active layer 220 a ofintrinsic amorphous silicon and an ohmic contact layer 220 b ofimpurity-doped amorphous silicon, a source electrode 233 and a drainelectrode 236. In FIGS. 4 and 5, the driving TFT DTr has a bottom gatestructure where the gate electrode 115 or 213 is positioned at a lowestlayer.

Meanwhile, each of the driving TFT DTr and the switching TFT may have atop gate structure where the semiconductor layer is positioned at alowest layer. Namely, as shown in FIG. 6, each of the driving TFT DTrand the switching TFT may include a semiconductor layer 313, whichincludes an active region 313 a of intrinsic poly-silicon andimpurity-doped regions 313 b at both sides of the active region 313 a,on a first substrate 310, a gate insulating layer 316, a gate electrode320 corresponding to the active region 313 a of the semiconductor layer313, an interlayer insulating layer 323 having semiconductor contactholes 325, which expose the impurity-doped regions 313 b of thesemiconductor layer 313, and source and drain electrodes 333 and 336respectively connected to the impurity-doped regions 313 b through thesemiconductor contact holes 325.

The top gate structure TFT requires the interlayer insulating layer 323in comparison to the bottom gate structure TFT. In the top gatestructure TFT, the gate line (not shown) is formed on the gateinsulating layer 316, and the data line (not shown) is formed on theinterlayer insulating layer 323.

Referring again to FIG. 4, a passivation layer 140, which includes adrain contact hole 143 exposing the drain electrode 136 of the drivingTFT DTr, is formed over the driving TFT DTr and the switching TFT. Forexample, the passivation layer 140 may be formed of an organicinsulating material, e.g., photo-acryl, to have a flat top surface.

A first electrode 150, which contacts the drain electrode 136 of thedriving TFT DTr through the drain contact hole 143, is formed on thepassivation layer 140 and separately in each pixel region P.

The first electrode 150 is formed of a conductive material having arelatively high work function, e.g., about 4.8 eV to 5.2 eV. Forexample, the first electrode 150 may be formed of a transparentconductive material such as indium-tin-oxide (ITO) to serve as an anode.

When the first electrode 150 is formed of the transparent conductivematerial, a reflection layer (not shown) may be formed under the firstelectrode 150 to increase emission efficiency in a top emission typeOLED display device. For example, the reflection layer may be formed ofa metallic material, such as aluminum (Al) or Al alloy such as AlNd,having a relatively high reflectivity.

With the reflection layer, the light from an organic emitting layer 155,which is formed on the first electrode 150, is reflected by thereflection layer such that the emission efficiency is increased. As aresult, the OLED display device has an improved brightness property.

A bank 153 having a double-layered structure, which includes a lowerlayer 153 a and an upper layer 153 b, is formed on the first electrode150 along boundaries of the pixel region P. The bank 153 overlaps edgesof the first electrode 150 such that a center of the first electrode 150is exposed by the bank 153.

The lower layer 153 a of the bank 153 has a hydrophilic property, andthe upper layer 153 b has a hydrophobic property.

The organic emitting layer 155 is formed in each pixel region Psurrounded by the bank 153 having the double-layered structure. Theorganic emitting layer 155 includes red, green and blue emittingmaterials in respective pixel regions P.

The organic emitting layer 155 is formed by forming an organic emittingmaterial layer and curing the organic emitting material layer. Theorganic emitting material layer is formed by coating, i.e., spraying ordropping a liquid phase organic emitting material by an ink jetapparatus or a nozzle-coating apparatus.

In the OLED display device 101 including the bank 153 of adouble-layered structure, which includes the lower layer 153 a havingthe hydrophilic property and the upper layer 153 b having thehydrophobic property, hydrophobic residues hardly remain on the firstelectrode 150 after patterning the bank 153, and the liquid phaseorganic emitting material can be spread well in the pixel region Psurrounded by the bank 153 when the material is sprayed or dropped.

Furthermore, since force drawing the organic emitting material isgenerated due to the lower layer 153 a having the hydrophobic property,the organic emitting material is spread better, and the organic emittinglayer 155 is formed in edges of the pixel region P adjacent to the bank153. Accordingly, the organic emitting layer 155 has a uniform thicknessin the pixel region P due to the bank 153 having the double-layeredstructure.

FIG. 4 shows a single-layered organic emitting layer 155. Alternatively,to improve emission efficiency, the organic emitting layer 155 may havea multi-layered structure. For example, the organic emitting layer 155may include a hole injecting layer, a hole transporting layer, anemitting material layer, an electron transporting layer and an electroninjecting layer stacked on the first electrode 150 as an anode. Theorganic emitting layer 155 may be a quadruple-layered structure of ahole transporting layer, an emitting material layer, an electrontransporting layer and an electron injecting layer or a triple-layeredstructure of a hole transporting layer, an emitting material layer andan electron transporting layer.

A second electrode 160 is formed on the organic emitting layer 155 andcovers an entire surface of a display region of the first substrate 110.The second electrode 160 is formed of a metallic material having arelatively low work function, e.g., Al, Al alloy such as AlNd, silver(Ag), magnesium (Mg), gold (Au), or Al—Mg alloy (AlMg). The secondelectrode 160 serves as a cathode.

The first electrode 150, the organic emitting layer 155 and the secondelectrode 160 constitute the emitting diode E.

A seal pattern (not shown) of a sealant or a frit material is formed onedges of the first substrate 110 or the second substrate 170. The firstand second substrates 110 and 170 are attached using the seal pattern. Aspace between the first and second substrates 110 and 170 has a vacuumcondition or an inert gas condition. The second substrate 170 may be aflexible plastic substrate or a glass substrate.

Alternatively, the second substrate 170 may be a film contacting thesecond electrode 160. In this instance, the film-type second substrateis attached to the second electrode 160 by an adhesive layer.

In addition, an organic insulating film or an inorganic insulating filmmay be formed on the second electrode 160 as a capping layer. In thisinstance, the organic insulating film or the inorganic insulating filmserves as the encapsulation film without the second substrate 170.

Hereinafter, a method of fabricating the OLED display device isexplained with reference to drawings.

FIGS. 7A to 7H are cross-sectional views showing a fabricating processof an OLED display device according to an embodiment of the presentinvention. The explanation is focused on a bank having a double-layeredstructure.

As shown in FIG. 7A, the gate line (not shown), the data line (notshown) and the power line (not shown) are formed on the first substrate110. In addition, the switching TFT (not shown) connected to the gateand data lines and the driving TFT DTr connected to the switching TFTand the power line are formed in the switching area (not shown) and inthe driving area DA, respectively.

As explained above, each of the switching TFT and the driving TFT DTrhas a bottom gate type TFT including the gate electrode 115 of FIG. 4 or213 of FIG. 5 as a lowest layer or a top gate type TFT including thesemiconductor layer 313 of FIG. 6 as a lowest layer. The bottom gatetype TFT includes the oxide semiconductor layer 120 of FIG. 4 or theamorphous silicon semiconductor layer 220 of FIG. 5 including the activelayer 220 a and the ohmic contact layer 220 b, and the top gate type TFTincludes the poly-silicon semiconductor layer 313 of FIG. 6.

Here, the switching TFT and the driving TFT DTr may be the bottom gatetype TFT including an oxide semiconductor layer. Therefore, the gateelectrode 115 of the driving TFT DTr is formed on the first substrate110, the gate insulating layer 118 is formed on the gate electrode 115,and the oxide semiconductor layer 120 is formed on the gate insulatinglayer 118 corresponding to the gate electrode 115. The etch-stopper 122is formed on the oxide semiconductor layer 120 and covers the center ofthe oxide semiconductor layer 120. The source and drain electrodes 133and 136 are formed on the etch-stopper 122 and spaced apart from eachother.

Next, an organic insulating material, e.g., photo-acryl, is coated overthe switching TFT and the driving TFT DTr and is patterned to form thepassivation layer 140 having a flat top surface and including the draincontact hole 143. The drain electrode 136 of the driving TFT DTr isexposed through the drain contact hole 143.

Next, a transparent conductive material, which has a relatively highwork function, is deposited on the passivation layer 140 and patternedto form the first electrode 150. The first electrode 150 contacts thedrain electrode 136 of the driving TFT DTr through the drain contacthole 143 and is separated in each pixel region P. For example, thetransparent conductive material may be indium tin oxide (ITO).

Meanwhile, as explained above, the reflection layer (not shown), whichincludes Al or Al alloy such as AlNd, may be formed under the firstelectrode 150 and on the passivation layer 140. The reflection layer maybe formed by the same mask process as the first electrode 150.

Next, as shown in FIG. 7B, a bank material layer 151 is formed on thefirst electrode 150 and the passivation layer 140. For example, the bankmaterial layer 151 may be formed by applying a bank material with acoating apparatus such as a spin-coating apparatus, a bar-coatingapparatus, or a slit-coating apparatus. The bank material may be aliquid phase and include a low molecular substance having a hydrophobicproperty and a high molecular substance having a hydrophilic propertymixed at an optimal content ratio. The bank material may also have aphotosensitive property and a phase separation property. For example,the low molecular substance may have a molecular weight of several tensto several thousand, more beneficially, more than 10 and under 10,000and include fluorine (F). The high molecular substance may have amolecular weight of ten thousand to several million, more beneficially,more than 15,000 and less than 1,000,000. The high molecular substancemay include a photosensitive polymer, for example, polyimide or acryl.

Next, in FIG. 7C, a heat-treatment process is performed to the bankmaterial layer 151 of FIG. 7B. The heat-treatment process may be asoft-baking process. For example, the bank material layer 151 of FIG. 7Bmay be heat-treated in an oven or furnace having an inside temperatureof 60 degrees of Celsius to 100 degrees of Celsius for several secondsto several hundred seconds or may be heat-treated on a hot plate havinga surface temperature of 60 degrees of Celsius to 100 degrees of Celsiusfor several seconds to several hundred seconds.

The bank material layer 151 of FIG. 7B is dried and cured by heatthrough the soft-baking process, and molecules actively move due to theheat. Thus, phase separation occurs. More particularly, relatively heavymolecules having molecular weights of more than 15,000 move to a lowerportion of the bank material layer 151 of FIG. 7B, and relatively lightmolecules having molecular weights under 10,000 move to an upper portionof the bank material layer 151 of FIG. 7B.

Meanwhile, solvents and moisture in the bank material layer 151 of FIG.7B are removed by the heat during the soft-baking process, and the banklayer 152 having the double-layered structure, which includes a firstlayer 152 a of a hydrophilic high molecular substance and a second layer152 b of a hydrophobic low molecular substance, is formed.

In FIG. 7D, an exposing mask (not shown) including a transmitting regionand a blocking region is disposed over the bank material layer 152 ofFIG. 7C, and an exposing process to the bank material layer 152 of FIG.7C is performed using the exposing mask without an additionalphotoresist layer.

Here, the bank material layer 152 of FIG. 7C is shown to have a negativetype photosensitive property where an exposed portion of the bankmaterial layer 152 of FIG. 7C remains after a developing process.Alternatively, the bank material layer 152 of FIG. 7C may have apositive type photosensitive property, and at this time, a position ofthe transmitting region and the blocking region is switched.

Next, the bank 153 including the lower layer 153 a and the upper layer153 b is formed by developing the bank layer 152 of FIG. 7C exposed tolight. In this instance, an exposed portion of the bank layer 152 ofFIG. 7C corresponding to the transmitting region of the exposing maskremains, and a non-exposed portion of the bank layer 152 of FIG. 7Ccorresponding to the blocking region of the exposing mask is removed bythe developing process.

Here, the first layer 152 a of the bank layer 152 of FIG. 7C contactingthe first electrode 150 does not include fluorine (F), and the secondlayer 152 b of the bank layer 152 of FIG. 7C including fluorine (F) doesnot contact the first electrode 150. Accordingly, after the developingprocess, fluorine residues may be completely removed or the minimum offluorine residues may remain on the surface of the first electrode 150even if the fluorine residues are not completely removed.

The bank 153 including the lower layer 153 a and the upper layer 153 bcorresponds to the boundaries of the pixel region P and overlaps theedges of the first electrode 150. The lower layer 153 a of the bank 153has a hydrophilic property, and the upper layer 153 b of the bank 153has a hydrophobic property.

In the meantime, the bank 153 having the double-layered structure may beformed using a photosensitive material having a hydrophilic property anda photosensitive material having a hydrophobic property. This will beexplained as another example of the embodiment with reference to FIGS.8A to 8E. FIGS. 8A to 8E are cross-sectional views showing a fabricatingprocess of on OLED display device according to another example of theembodiment of the present invention. In FIGS. 8A to 8E, the switchingand driving TFTs and layers under the first electrode 150 are omitted,and figures show cross-sections of the OLED display device in steps offorming a bank having a double-layered structure.

As shown in FIG. 8A, a first bank material layer 451 is formed on thefirst electrode 150 all over the first substrate 110. The first bankmaterial layer 451 may be formed by applying a photosensitive materialhaving a hydrophilic property, for example, polyimide or acryl, using acoating apparatus (not shown).

Next, in FIG. 8B, a first bank layer 452 having the hydrophilic propertyis formed by drying and curing the first bank material layer 451 of FIG.8A through a heat-treatment process, for example, the soft-bakingprocess as mentioned above.

The photosensitive material having the hydrophilic property may includea high molecular substance or a low molecular substance.

In FIG. 8C, a second bank material layer 453 is formed on the first banklayer 452. The second bank material layer 453 may be formed by applyinga photosensitive material having a hydrophobic property, for example,acryl including fluorine (F), using a coating apparatus (not shown).

Next, in FIG. 8D, a second bank layer 454 having the hydrophobicproperty is formed by drying and curing the second bank material layer453 of FIG. 8C through a heat-treatment process, for example, thesoft-baking process as mentioned above. The photosensitive materialhaving the hydrophobic property may include a high molecular substanceor a low molecular substance.

Since the first bank layer 452 having the hydrophilic property isalready cured, molecules of the photosensitive material having thehydrophobic property do not move into the first bank layer 452 duringthe soft-baking process of the second bank material layer 453 of FIG.8C.

In FIG. 8E, the first and second bank layers 452 and 454 of FIG. 8D areexposed to light through an exposing mask (not shown) and developed,thereby forming the bank 153 having a double-layered structure of thehydrophilic lower layer 153 a and the hydrophobic upper layer 153 b,which is the same as that in FIG. 7D.

In another example of the embodiment of the present invention, there isno hydrophobic residue on the first electrode 150, and thus an organicemitting material, which will be sprayed or dropped, is spread well.

In the meantime, as shown in FIG. 7E, after forming the bank 153 havingthe double-layered structure, an organic emitting material layer 154 isformed on the first electrode 150 by spraying or dropping a liquid phaseorganic emitting material in a region surrounded by the bank 153, i.e.,in the pixel region P, with an ink jet apparatus or a nozzle-coatingapparatus 198.

Even if the organic emitting material is sprayed or dropped on the upperlayer 153 b because of a mis-alignment of the ink jet apparatus or thenozzle-coating apparatus 198, the organic emitting material isconcentrated into a center of the pixel region P because the upper layer153 b has the hydrophobic property. In addition, even if an excessiveamount of the organic emitting material is sprayed or dropped, theorganic emitting material does not flow over the upper layer 153 b dueto the hydrophobic property of the upper layer 153 b.

Furthermore, since the lower layer 153 a of the bank 153 has thehydrophilic property, force drawing the liquid phase organic emittingmaterial is generated from sides of the lower layer 153 a of the bank153, and the liquid phase organic emitting material is spread well onthe first electrode 150 to contact the sides of the lower layer 153 a ofthe bank 153.

Next, as shown in FIG. 7F, by performing a curing process, solvents andmoisture in the organic emitting material layer 154 of FIG. 7E areremoved such that the organic emitting layer 155 is formed in the pixelregion P.

As mentioned above, since the organic emitting layer 155 contacts thesides of the lower layer 153 a of the bank 153, the organic emittinglayer 155 is also formed around the bank 153 and has a substantiallyuniform thickness in the pixel region P.

Here, the organic emitting layer 155 has a single-layered structure.Alternatively, to improve emission efficiency, the organic emittinglayer 155 may have a multi-layered structure, which may be formed by thesame method as that of the single-layered structure or may be formed inan entire surface of a display region by a deposition method. Forexample, the organic emitting layer 155 may include a hole injectinglayer, a hole transporting layer, an emitting material layer, anelectron transporting layer and an electron injecting layer stacked onthe first electrode 150 as an anode. The organic emitting layer 155 maybe a quadruple-layered structure of the hole transporting layer, theemitting material layer, the electron transporting layer and an electroninjecting layer or a triple-layered structure of the hole transportinglayer, the emitting material layer and the electron transporting layer.

Next, as shown in FIG. 7G, the second electrode 160 is formed on theorganic emitting layer 155 by depositing a metallic material having arelatively low work function. The second electrode 160 is formed on anentire surface of the display region. The metallic material includes atleast one of Al, Al alloy such as AlNd, Ag, Mg, Au and AlMg.

As explained above, the first electrode 150, the organic emitting layer155 and the second electrode 160 constitute the emitting diode E.

Next, as shown in FIG. 7H, after forming a seal pattern (not shown) onedges of the first substrate 110 or the second substrate 170, the firstand second substrates 110 and 170 are attached under a vacuum conditionor an inert gas condition such that the OLED display device isfabricated. Alternatively, a paste seal (not shown), which is formed ofa fit material, an organic insulating material or a polymer materialhaving transparent and adhesive properties is formed over an entiresurface of the first substrate 110, and then the first and secondsubstrates 110 and 170 are attached. As explained above, instead of thesecond substrate 170, an inorganic insulating film or an organicinsulating film may be used for an encapsulation and may be attached byan adhesive layer.

In the OLED display device of the invention, since the bank has thedouble-layered structure of the hydrophilic lower layer and thehydrophobic upper layer, the hydrophobic residues hardly remain on thefirst electrode after forming the bank by patterning the bank layer.Therefore, the liquid phase organic emitting material is spread well inthe pixel region surrounded by the bank when it is sprayed or dropped.

Moreover, the organic emitting material is spread better due to theforce drawing the organic emitting material from the lower layer of thebank because the lower layer of the bank has the hydrophilic property,and the organic emitting layer is formed in the boundaries of the pixelregion P adjacent to the bank.

Accordingly, the organic emitting layer has a uniform thickness in thepixel region, and the organic emitting layer is prevented from beingdegraded, thereby lengthening lifetime of the device.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the spirit or scope of the invention. Thus, it isintended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

What is claimed is:
 1. A method of fabricating an organic light emittingdiode display device, comprising: forming a thin film transistor (TFT)on a first substrate, including a gate insulating layer between a gateelectrode and a semiconductor layer, the gate insulating layer coveringan entire surface of the first substrate including any TFT electrodeformed on the first substrate, wherein the forming of the TFTcomprising: depositing a single region of oxide semiconductor layerabove the gate electrode which is separated by the gate insulatinglayer, wherein the single region of oxide semiconductor layer has anarrower width than the gate electrode; depositing an etch stopper layerto directly cover and overlap a center portion of the single region ofoxide semiconductor layer, such that the etch stopper layer separatesand divides remaining uncovered portions of the single region of oxidesemiconductor layer into a first exposed portion and a second exposedportion of the single region of oxide semiconductor layer; depositingrespectively, a source electrode over the first exposed portion and adrain electrode over the second exposed portion of the single region ofoxide semiconductor layer; forming a passivation layer over the TFThaving a planar surface covering an entire surface of the displaydevice; forming a first electrode over the passivation layer including adisplay region, which includes a plurality of pixel regions, the firstelectrode formed in each of the plurality of pixel regions, the firstelectrode connecting to the drain electrode of the TFT through a holeformed in the passivation layer; applying a bank material in a liquidphase on the first electrode, the bank material including a mixture of alow molecular substance having a hydrophobic property and a highmolecular substance having a hydrophilic property; drying and curing thebank material to separate the low molecular substance from the highmolecular substance, thereby forming a first bank layer including thehigh molecular substance and a second bank layer including the lowmolecular substance on top of the first bank layer; removing a portionof the first bank layer and the second bank layer to expose the firstelectrode, thereby forming a bank on edges of the first electrode andsurrounding each of the plurality of pixel regions; forming an organicemitting layer on the first electrode and in each of the plurality ofpixel regions surrounded by the bank; and forming a second electrode onthe organic emitting layer, the second electrode covering the entiresurface of the display region; wherein the first electrode overlaps aportion of the gate electrode; and wherein the first electrode of afirst pixel region is spaced apart from a gate electrode of a TFT of asecond pixel region and overlaps a source electrode of the TFT of thesecond pixel region.
 2. The method according to claim 1, wherein thehigh molecular substance has a molecular weight of more than 15,000, andthe low molecular substance has a molecular weight under 10,000.
 3. Themethod according to claim 2, further comprising patterning the first andsecond bank layers by light-exposing and developing the first and secondbank layers.
 4. The method according to claim 2, wherein the highmolecular substance includes polyimide or acryl, and the low molecularsubstance includes fluorine of 1 to 10 wt %.
 5. A method of fabricatingan organic light emitting diode display device, comprising: forming athin film transistor (TFT) on a first substrate, including a gateinsulating layer between a gate electrode and a semiconductor, the gateinsulating layer covering an entire surface of the first substrateincluding any TFT electrode formed on the first substrate, wherein theforming of the TFT comprising: depositing a single region of oxidesemiconductor layer above the gate electrode which is separated by thegate insulating layer, wherein the single region of oxide semiconductorlayer has a narrower width than the gate electrode; depositing an etchstopper layer to directly cover and overlap a center portion of thesingle region of oxide semiconductor layer, such that the etch stopperlayer separates and divides remaining uncovered portions of the singleregion of oxide semiconductor layer into a first exposed portion and asecond exposed portion of the single region of oxide semiconductorlayer; depositing respectively, a source electrode over the firstexposed portion and a drain electrode over the second exposed portion ofthe single region of oxide semiconductor layer; forming a passivationlayer over the TFT having a planar surface covering an entire surface ofthe display device; forming a first electrode over the passivation layerincluding a display region, which includes a plurality of pixel regions,the first electrode formed in each of the plurality of pixel regions,the first electrode connecting to the drain electrode of the TFT througha hole formed in the passivation layer; forming a bank on edges of thefirst electrode and surrounding each of the plurality of pixel regions,the bank including a first bank layer and a second bank layer; formingan organic emitting layer on the first electrode and in each of theplurality of pixel regions surrounded by the bank; and forming a secondelectrode on the organic emitting layer, the second electrode coveringan entire surface of the display region, wherein forming the first banklayer on the first electrode includes applying a liquid phase materialhaving a hydrophilic property and performing a heat-treatment process tothereby dry and cure the first bank layer, wherein forming the secondbank layer on the first bank layer includes applying a liquid phasematerial having a hydrophobic property and performing a heat-treatmentprocess to thereby dry and cure the second bank layer, wherein the firstbank layer does not include fluorine and the second bank layer includesfluorine, wherein the first electrode overlaps a portion of the gateelectrode, and wherein the first electrode of a first pixel region isspaced apart from a gate electrode of a TFT of a second pixel region andoverlaps a source electrode of the TFT of the second pixel region.